Hydroxypivalaldehyde (hereinbelow, HPA) is a raw material for neopentyl glycol (hereinbelow, NPG). HPA is also used as a raw material for acetal compounds such as spiroglycol (hereinbelow, SPG). When HPA is subjected to hydrogenation reaction (hereinbelow, hydrogenation), for example, NPG is obtained. From HPA and a polyhydric alcohol, an acetal compound such as SPG is obtained. MPG is used as a raw material for alkyd resin paints, polyester resins, and powdered paints. SPG is used as an antioxidant and also as a raw material for highly heat resistant resin.
HPA is generally obtained by an aldol reaction of isobutyraldehyde (hereinbelow, IBAL) with formaldehyde (hereinbelow, FA) under basic conditions. In this case, HPA contains, as impurities, NPG, FA, a catalyst used in the reaction, and a carboxylate salt such as formate salt which is produced as byproduct, as described in Patent Literature 1 and the like. As described in Patent Literature 1 and the like, it is known that these impurities inhibit hydrogenation when NPG is produced.
In Patent Literature 2, it is mentioned that impurity of aldehydes such as IBAL and FA, which are contained in HPA when SPG is produced, influences the quality of SPG. Thus, purification for obtaining highly pure HPA is required.
As methods of removing impurities contained in HPA, crystallization, extraction, and distillation have been reported. For example, in Patent Literature 1, a process of purifying HPA by crystallization is described. By this method, HPA having the purity more than 98% by mass can be obtained. In Patent Literature 3, in order to remove carboxylate salts contained in the reaction liquid after HPA is synthesized, an operation similar to extraction is carried out. Water is added to the reaction liquid, which is cooled and then allowed to separate into two layers. Carboxylate salts are removed by partitioning HPA into the oil layer and the carboxylate salts into the water layer.
In Patent Literature 4, a process of removing low-boiling-point impurities by distillation is described. Additionally, as a method including extraction and distillation in combination, a process in which extraction by octanol is carried out to remove organic acid salt and then low-boiling-point impurities are removed by distillation is described in Patent Literature 5.